B1559 — Door Lock Cylinder Circuit Failure

Is it safe to drive with B1559?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

What is the most common cause of B1559?

The most common causes are: faulty switch, motor or actuator of the affected system, body control module (BCM) fault, damaged wiring in door jambs or wet areas.

How much does it cost to fix B1559?

Replace the switch or actuator — $120–$450; Repair wiring or connectors — $80–$250; BCM repair or replacement — $300–$900. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will B1559 clear itself?

Sometimes B1559 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What are the symptoms of B1559?

Drivers most often notice: the affected function (locks, windows, lighting, wipers) works intermittently or not at all, warning light on the dashboard, no impact on engine operation in most cases.

When your vehicle's body control module detects that the door lock cylinder circuit isn't responding the way it should, it logs diagnostic trouble code B1559. This code falls within the B-series classification, which covers body and comfort system faults rather than engine or transmission problems. The literal translation of B1559 is "Door Lock Cylinder Circuit Failure" — meaning the electrical pathway controlling your door lock mechanism has stopped working correctly.

Modern vehicles rely on a network of modules that communicate over data buses. When you turn the key or press the lock button, a signal travels from the door lock cylinder switch through the wiring harness to the body control module, which then activates the lock actuator motor. The BCM acts as the traffic controller for these body functions. If that signal never arrives, or if the return signal confirms a problem, the module flags B1559. The ECU doesn't set this code based on a single glitch — it waits for the fault to appear repeatedly under specific conditions before triggering the warning light, which is why the freeze frame data captured alongside B1559 is so useful for diagnosis.

Symptoms of B1559

• The door lock mechanism stops responding to the key cylinder or interior switch, or operates only intermittently
• A dashboard warning light illuminates, though in some cases no light appears depending on the vehicle's programming
• The affected function may work in one direction (lock) but not the other (unlock), indicating a partial circuit failure
• No effect on engine performance, transmission operation, or braking systems — B1559 is purely a body control issue
• Power door locks may work from the driver's door but not the passenger doors, pointing toward a specific circuit problem
• In some configurations, the remote keyless entry system continues working even when the physical cylinder switch fails, since those operate on different signal paths

Common Causes

The most frequent culprits behind B1559 are the simplest components in the circuit. A worn-out door lock switch, a motor that has seized internally, or an actuator with stripped gears will prevent the lock mechanism from functioning. Wiring damage ranks second — the door jamb areas experience constant flexing every time you open and close the door, and the insulation can crack over time. Water intrusion accelerates connector corrosion, particularly in vehicles that see heavy rain or automatic car washes regularly. A faulty body control module can also trigger B1559, though this is less common than component-level failures. Finally, a blown fuse or failed relay feeding the door lock circuit will produce identical symptoms with no physical damage to switches or motors.

How to Diagnose B1559

1. Plug in a quality OBD2 scanner and retrieve all stored codes. Document the freeze frame data that accompanied B1559 — this snapshot records engine load, RPM, coolant temperature, and vehicle speed at the moment of failure. These conditions are your target when road-testing later.
2. Look for any related diagnostic trouble codes. Body control systems often store secondary codes that point more directly to the failed component. Also search for technical service bulletins specific to your make, model, and model year — manufacturers sometimes publish software updates or known fixes for recurring issues.
3. Perform a thorough visual inspection of the wiring between the door lock cylinder and the BCM. Focus on the boot where wiring passes through the door hinge pillar — this is the most vulnerable point for broken wires. Pull connectors apart and examine pins for corrosion, bent contacts, or moisture residue.
4. Test the circuit with a multimeter while operating the lock mechanism. You should see voltage变化 at the actuator when commanding locks on and off. No voltage indicates an open circuit upstream; constant voltage with no movement suggests a ground problem or failed motor.
5. If the wiring checks out, verify the body control module's output signals using a scan tool capable of bidirectional control. Many professional-grade scanners allow you to command the door locks directly from the tool, isolating whether the problem lies in the switch, the module, or the actuator.
6. Clear B1559 after repairs, then complete a full drive cycle including the specific conditions from the freeze frame data. The code must not return before considering the repair complete.

Repair Options and Costs

Switch or Actuator Replacement — $120–$450: If testing confirms the motor has failed or the switch contacts are worn, replacement of the failed component resolves B1559. Actuators are sold as complete assemblies in most cases, while switches may be replaced individually or as part of a door panel trim piece.

Wiring or Connector Repair — $80–$250: Broken wires can often be spliced and sealed rather than replaced entirely. Corroded connectors can be cleaned with electrical contact cleaner and protected with dielectric grease. In severe cases, replacing the connector terminals or the entire harness section may be necessary.

BCM Repair or Replacement — $300–$900: When the module itself is at fault, options include sending it for rebuild, purchasing a used unit from a salvage yard (requiring programming), or buying a new replacement from the dealer (typically the most expensive route).

Total repair costs for B1559 typically range from $80 to $900 depending on which component failed. Begin troubleshooting with the least expensive possibilities — switches and wiring — before investing in a replacement body control module.

Driving Safety Verdict

Severity: Short — generally safe to drive. B1559 does not affect engine operation, braking, steering, or crash safety systems. The primary concern is convenience and security: if your door locks are inoperative, the vehicle cannot be secured against theft. Exterior lighting failures related to body circuit faults would present a safety issue during night driving or poor visibility conditions. Wiper motor failures linked to shared BCM circuits create hazard visibility problems in rain or snow. Address B1559 promptly if it involves locking or lighting; otherwise, scheduling repair at your convenience is acceptable.

Related OBD2 Codes

• B1500: Lamp Turn Signal Left Circuit Open
• B1501: Lamp Turn Signal Left Circuit Short To Battery
• B1502: Lamp Turn Signal Left Circuit Short To Ground
• B1503: Lamp Turn Signal Right Circuit Failure
• B1504: Lamp Turn Signal Right Circuit Open
• B1505: Lamp Turn Signal Right Circuit Short To Battery